Thanks! Unfortunately, it doesn't work in this case...
(As a side note, I mounted the diag partition of the device, and found various test scripts on it, which I've tried. The touch screen works, as well as the buttons. I found a factory_reset.sh script, which also resets the time. Without effect.) If there is a hidden pastlog area, is there any way to retrieve this log from the device to study what is going wrong during boot?

If you can access diag partition, you can access the raw partition as well...

Another possibility is to manually install the enable-adb package and connect to computer during startup - if you are lucky, adb already is running when spinning arrows occur and you can log into adb shell...

Ok, I've dd-ed the LOG area of the start partition. I suspect this may be the culprit: the messages that repeat over and over again - till the reset button is pressed - are "Unable to attach mixer to device default: No such file or directory", "AudioPolicyService not published, waiting..." and "external/alsa-lib/src/control/control.c:902snd_ctl_open_noupdate) Invalid CTL AndroidOut".

When I check the log file posted earlier in this thread, I have the impression that during boot there should be a message "#0: imx-3stack (CS42L52 codec)" below "ALSA device list"; however, in my case it prints "No soundcards found."

This could be an indication that the audio hardware is no longer working and the software is stuck in a loop waiting for an AudioPolicyService to start.

Could there be a way to disable audio? I don't need audio on my e-reader. Or is this hard wired in the kernel and virtually impossible to disable? (Sorry for asking so much - I am not very familiar with Android, although I know a little about Linux.)

My last hint is ADB. At rotating arrows screen you should be able to log in via ADB shell - but only if ADB has been is installed and USB debugging has been enabled. You can install it manually - just have a look at the do_update.sh script in the enableadb package. And you can then enable USB debugging by editing /default.prop